Early childhood is a critical period for establishing healthy diet and physical activity behaviors that may influence children's short- and long-term risk for obesity and other chronic diseases. Unfortunately, during this important stage of development, many preschool children have already adopted unhealthy diet and physical activity behaviors. Home and child care are two important spheres of influence that shape young children's diet and physical activity behaviors. Interventions engaging both spheres in a coordinated effort would ensure that children receive consistent health messages. There have been very few interventions that have targeted the child care setting, many of which made no attempt to engage parents. Those that did include a parent component generally used low-intensity strategies (e.g., newsletters, homework assignments). Innovative approaches that engage both the child care center and parents in a substantial and meaningful way are needed. Social marketing has been identified as a promising approach for health promotion efforts targeting children. Social marketing principals recognize the need to engage all individuals whose behaviors must be affected to bring about change, and to offer messages that emphasize benefits, and overcome barriers associated with behavior change. The application of social marketing principles in child care-based interventions is very limited. The proposed study is a two-arm, randomized controlled trial (86 centers and 860 children) to evaluate the effect of a 12-month intervention - Our Year of Healthy Living - on the diet and physical activity behaviors of preschool children (3-4 years) and their adult caregivers (parents and child care providers). The intervention will use a series of social marketing campaigns initiated in the child care center that incorporate visual cues, educational materials, activities, contests, and e-messages to deliver targeted messages. This study's primary outcomes are children's minutes of non-sedentary activity (measured via accelerometers) and diet quality (assessed with Healthy Eating Index scores). Secondary outcomes will assess: children's body mass index, food and physical activity practices in the child care center and at home, and health behaviors of child care providers and parents.